Molecular recognition based on roof-shaped diol hosts. X-ray crystal structures of inclusion compounds with methanol, pyridine and toluene

Three crystalline inclusion compounds of roof-shaped trans-11,12-bis(diaryl -hydroxymethyl)-9,10-dihydro-9,10-ethanoanthracene host molecules [where ar yl is 4-methyl-phenyl (3) or 4-t-butylphenyl (4)] have been studied by X-ra y diffraction. The crystals of both the 3 . methanol (2 : 1) [a = 10.755(1) , b = 11.571(1), c = 14.697(2) Angstrom, alpha = 75.12(1), beta = 89.67(1), gamma = 87.13(1) degrees] and the 4-pyridine (2 : 3) compounds [a = 14.045 (3), b = 14.366(3), c = 15.607(3) Angstrom, alpha = 91.62(1), beta = 103.65 (1) and gamma =116.05(1)degrees] are triclinic (P-1), while the 3 . toluene (1 : 1) complex has orthorhombic ( Fddd) symmetry [a = 16.041(1), b = 25.0 08(1), c = 40.440(4) Angstrom]. The host-guest interactions in both triclin ic crystals are characterised by hydrogen bonds, with different patterns ho wever. The determined crystal structures indicate a compromise between the requirement of hydrogen bonding on the one hand and close packing on the ot her. The highly symmetrical host framework in the toluene (1 : 1) complex o f 3 seems to be the result of shape recognition, although a tendency toward s weak (C-methyl)H ... pi(aryl) interactions [C-methyl ... pi = 3.533(7) an d 3.674(6) Angstrom] between the hosts was observed. The present roof-shape d diol hosts give excellent examples of molecular recognition by exhibiting two significantly different conformations, mostly depending on the proton donor/acceptor ability of the guest component. (O)H ... O intramolecular bo nding between the two alcoholic groups characterises the so-called active f orm, whereas weaker (O)H ... pi and pi ... pi interactions stabilise the `i nactive' conformation.